I love the Finis SwiMP3 player. It’s fantastic for relieving the boredom of swimming up and down the pool and sound quality underwater is surprisingly good thanks to its use of bone-conduction technology.
Humans normally hear through air conduction, but because there is no air underneath the water, Finis claims that bone conduction provides the clearest sound quality possible. Instead sound vibrations are transferred from the cheek bone to the inner ear, giving the swimmer much better sound quality. Certainly audio quality is much better than other underwater MP3 players I’ve tested including Speedo’s much cheaper Aquabeat.